The present invention relates to a blood filtration unit which is to be implanted inside a vessel of a patient's body.
Currently known filtration units are formed by at least one filter which is implanted intravenously, generally into the inferior vena cava, to capture blood clots which could migrate towards the heart, in order to avoid the risk of embolism.
Traditionally, blood filters have been classified in two categories: permanent filters and temporary, or retrievable, filters.
Permanent filters are designed to be implanted permanently in patients where the risk of embolism is chronic. Some conventional permanent filters have, for example, a frustoconical structure comprising a series of branches terminated by barbs, anchors or similar structures which enable the filter to be secured permanently to the vessel wall. Long-term risks associated with implantation of a permanent vena cava filter include venous stasis due to caval occlusion and its related complications. Although long term complication rates with permanent filters in patients are low, these can be avoided with the use of retrievable or temporary filters in patients with indications such as after severe trauma, and prior to extensive orthopedic or pelvic surgery.
Temporary filters are designed to be implanted temporarily in patients where the risk of blood clot migration lasts only for a brief period, usually a few weeks. Temporary filters differ from permanent filters basically in that they do not comprise hooks for securing to the vessel wall. The branches of the filter simply engage the vessel wall without hooking into it. Several temporary filtering devices have been developed for insertion into the inferior vena cava (IVC) by transcatheter technique.
Temporary filters are further classified as either tethered temporary or retrievable filters. Tethered temporary filters are modified catheters or intraluminal devices attached to a tethering catheter or a wire for retrieval one to six weeks after implantation. Tethered filters remain connected throughout the entire period of implantation to prevent the filter from migrating in the vessel. They are implanted in the infrarenal vena cava with the tethering catheter extending out of the puncture site in the neck or groin, or buried subcutaneously within the soft tissues in the patient's neck. The tether remains coupled to the filter after deployment and is later used to retrieve the filter. The potential for septic complications associated with the tethering catheter exiting the neck or groin require removal of such devices within fourteen days of placement. Risk periods for pulmonary embolism in such patients, however, can extend up to twenty-one weeks.
Retrievable filters are usually self-expanding and self-attaching devices which can be removed or, if desired, left in place permanently. Typically, these filters have a construction similar to some versions of permanent filters. A hook or similar grasping structure is provided to allow a snare to engage the filter during the retrieval procedure. The filter in its entirety is then retrieved using a snare by drawing it into a catheter. However, to ensure the filter does not migrate within the vessel, barbs, anchors or similar structures must be used to engage the filter with the interior wall of the vessel for retaining the filter in place. These anchors make removal without injuring the vessel difficult. Percutaneous retrieval of these devices requires a new jugular and/or femoral vein catheterization. There is approximately a two week period for removal or repositioning of the filter before it becomes fixed to the caval wall by endothelization. Most existing filters are not easily or safely removable after they have remained in place for more than two weeks, and consequently longer term temporary filters which do not result in the likelihood of injury to the vessel wall upon removal are not available.
In some patients, the risk of embolism remains great and continues over time contrary to what was expected. If a temporary filter has been implanted first, it is generally necessary to remove the filter in order to replace it by a permanent filter if the two week time period for removal or repositioning of the filter has been exceeded.
These problems are overcome through the use of a filter having a broad range of clinical utility with a long-term implantation period and at the same time a long-term retrievability option.